1. Field of the Invention
The present invention relates to an actuator using an electromechanical transducer, particularly to an actuator using an electromechanical transducer suitable for finely positioning an optical system of a lens or the like.
The present invention also relates to an apparatus such as an optical system which employs an actuator using an electromechanical transducer.
2. Prior Art
When a drive pulse having a waveform comprising a gradual rise portion and a steep fall portion successive thereto is applied to a piezoelectric element, gradual elongation is caused in the thickness direction of the piezoelectric element at the gradual rise portion of the drive pulse and rapid contraction is caused at the steep fall portion. Hence, there is known an actuator of a linear type in which by using the characteristic, charge and discharge are repeated at different speeds by applying a drive pulse having the above-described waveform to a piezoelectric element and a drive shaft member fixedly attached to the piezoelectric element is reciprocated at different speeds by generating oscillation in the thickness direction having different speeds at the piezoelectric element thereby moving a moving member frictionally coupled to the drive shaft member in a predetermined direction.
According to the above-described actuator of a linear type using a piezoelectric element, there have been pointed out problems of transmission efficiency where a drive force transmitted from the piezoelectric element is not efficiently transmitted to a drive shaft member by elasticity of an adhesive agent since the drive shaft member is coupled to the piezoelectric element by adhesion, and a problem in reliability where an adheringly coupled portion is liable to peel off and so on. Further, there has been pointed out a problem of a difficulty in assembling steps where careful attention is needed in coupling the drive shaft member with the piezoelectric element such that no deviation or inclination of an axis is caused, and the like.
Further, according to the above-described linear type actuators using a piezoelectric element, a frictonally coupled portion for coupling the drive shaft member with the moving member is frictionally coupled previously by a predetermined constant force. When the drive shaft member is reciprocated at different speeds, in the case of motion having slow speed, the moving member is moved in a predetermined object direction under a state where the drive shaft member and the moving member are frictionally coupled. In the case of motion in an opposed direction having a fast speed, slip is caused at the frictionally coupled portion by inertia of the moving member, and the moving member tends to stay at the position.
By repeating the reciprocating motion of the drive shaft member at different speeds, the moving member is moved in the predetermined object direction while causing a slip between the drive shaft member and the moving member. Hence, a portion of the drive energy applied to the drive shaft member is dissipated by the slip caused between the drive shaft member and the moving member, and the drive efficiency is not excellent.
Further, according to the above-described linear type actuators using a piezoelectric element, a side of the drive shaft member opposed to a side where the piezoelectric element is fixedly attached constitutes a free end and accordingly, although the drive shaft member can be oscillated in the axial direction by the oscillation of the piezoelectric element in the thickness direction, at the same time, oscillation in a direction orthogonal to the axial direction is also caused in the drive shaft member. Therefore, this causes the inconvenience that not only is the efficiency of the actuator lowered, but noise is generated.
Further, an oscillation wave in the axial direction is transmitted to the drive shaft member and reflected by the free end. Accordingly, a reflected wave and the oscillation wave transmitted from the piezoelectric element to the drive shaft member interfere with each other, as a result, the waveform of the drive pulse transmitted from the piezoelectric element to the drive shaft member is distorted and the driving operation cannot be carried out efficiently.
Further, there is a problem in reliability and the transmission efficiency of an applied force. The mechanical strength is not sufficient because one end of the drive shaft member is a free end, and since the piezoelectric element and the drive shaft member are coupled by adhesion, an adheringly coupled portion is liable to peel off. Furthermore, there has been the problem that the number of assembling steps is large.